This invention relates to a burner and process for operating gas turbines with minimal emissions of air pollutants, especially nitrogen oxides (NO.sub.x). More particularly, the burner and process permit operation of gas turbine combustors at high excess air and at elevated pressure.
The development of a compact burner that would fit in the castings of gas turbines and yield combustion products with a limited content of atmospheric pollutants [NO.sub.x, carbon monoxide (CO) and unburned hydrocarbons (UHC)] has long failed to deliver a commercially acceptable product. In 1981, U.S. Pat. No. 4,280,329 of Rackley et al disclosed a radiant surface burner in the form of a porous ceramic V-shaped element. Theoretically, the proposed burner was attractive but, practically, it had serious deficiencies, such as fragility, high pressure drop therethrough and limited heat flux. No advance in the art of radiant surface combustion for gas turbines has appeared since the Rackley et al proposal.
Efforts to minimize atmospheric pollutant emissions from the operation of gas turbines have been directed in different approaches. U.S. Pat. Nos. 4,339,924; 5,309,709 and 5,457,953 are illustrative of proposals involving complicated and costly apparatus. Catalytica Inc. Is promoting a catalytic combustor for gas turbines which reportedly (San Francisco Chronicle, Nov. 21, 1996) is undergoing evaluation. None of the proposals provide simple, compact apparatus and catalysts are expensive and have limited lives.
A principal object of this invention is to provide compact burners for gas turbines which feature surface-stabilized combustion conducted at high firing rates with high excess air to yield minimal polluting emissions.
Another important object is to provide burners for gas turbines which permit broad adjustment of heat flux.
A related object is to provide compact burners with low pressure drop and stable operation over a broad pressure range and excess air variation.
Still another object is to provide burners for gas turbines which have simple and durable construction.
A further primary object of the invention is to provide a method of operating gas turbines to yield combustion products with a very low content of atmospheric pollutants.
These and other features and advantages of the invention will be apparent from the description which follows.